# CVE-2021-47156: Security feature bypass in n/a

> Attackers can bypass IP-based access controls by using IP addresses with extraneous zero characters in the Net::IPAddress::Util Perl module.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 Mar 2024
- **Updated:** 27 Mar 2025
- **Also known as:** GHSA-42vc-w257-pp26

## What is CVE-2021-47156?

CVE-2021-47156 is a medium-severity vulnerability in n/a, published on 18 Mar 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The Net::IPAddress::Util module before 5.000 for Perl does not properly consider extraneous zero characters in an IP address string, which (in some situations) allows attackers to bypass access control that is based on IP addresses.

Weakness: CWE-1287 (Improper Validation of Specified Type of Input)

## Which versions are affected by CVE-2021-47156?


## How do I fix CVE-2021-47156?

No fix has been published for CVE-2021-47156 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-47156 being exploited?

There is no known exploitation of CVE-2021-47156 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-47156 and fix it if it is affected.

What it is: CVE-2021-47156 is a medium-severity vulnerability in n/a, published on 18 Mar 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-47156 in the wild and no public exploit code.

Affected product: n/a. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-47156/ (Markdown: https://insights.sbomify.com/CVE-2021-47156/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47156
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47156
- OSV: https://osv.dev/vulnerability/CVE-2021-47156

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47156/
Summaries are generated and may contain mistakes; the official description above is the record.